It is, of course, well known to make food packaging trays of molded wood pulp, and also of foam plastic, e.g., polystyrene. Particularly, the molded wood pulp food trays have served the food packaging industry well for many years. Such wood pulp trays have the advantage, besides low price and cost to the consumer, of being clean, sturdy and safe; of being biodegradeable so as to minimize the problem of solids pollution; of being soft and relatively flexible so as to protect and prevent bruising of food products such as fresh fruit and tomatoes; and of being capable of controlling excess moisture. In contrast, foam polystyrene has only some of these advantages while transparent plastic normally has none of these advantages.
Indeed, these clear plastic trays have many defects, some shared with foam plastic trays, including reduced strength, increased cost, use of our valuable petroleum resources, fabrication of non-biodegradeable material, and hard surfaces and sharp edges which bruise and cut the fruit. In addition, such plastic trays do not breathe, i.e., permit passage therethrough of air and water vapor, and more importantly they also collect moisture in puddles, thereby encouraging discoloration and rotting; in addition, any moisture which accumulates then serves to opacify the package itself, thereby contributing to the very problem of lack of visibility through the bottom wall which such trays were originally designed to overcome.
Food packaging trays have evolved substantially over the years. Earlier trays had essentially straight side walls and a flat peripheral lip, and these served the industry successfully for many years, particularly for the packaging of meat. In more recent years, such earlier trays were used for the packaging of produce, such as a half dozen deluxe apples or oranges, provided with a transparent film overwrap. However, as the nature of transparent plastic wrap film changed and nonelastic cellophane was replaced with more elastic thermoplastic overwrap films, the trays in accordance with the Reifers U.S. Pat. No. 3,185,371 was developed, and this tray became the leader in the field. In more recent years, there has been an increase in a desire for greater visibility of the food packages.
Among the unsuccessful attempts to provide a produce tray formed of opaque material such as wood pulp was to simply take a conventional solid bottom tray and die cut openings in the bottom wall. This was not found to be a successful approach to the problem because the resultant tray was too weak and it was also unstable to warpage. In addition, the die-cutting operation, even if carried out on an adherently soft and flexible material, inevitably produces sharp edges which can cut or bruise sensitive produce. This is a particularly acute problem in the packaging of produce because even a very slight edge or roughness can cause an undesirable indentation in soft fruit, even if the skin of the fruit is not broken.
The Reifers et al. U.S. Pat. No. 3,682,365 presents a good description of the evolution of one-use, throw-away food packaging trays formed of opaque material and having bottom wall visibility by the provision of openings in the bottom wall. The Bixler U.S. Pat. No. 3,698,623 discloses such a meat packaging tray having inverted V-shaped ribs. The Reifers et al. U.S. Pat. Nos. 3,718,274 and 3,764,057 show highly successful commercial embodiments of such meat packaging trays with open-window bottom walls.
However, it will be understood that while such constructions, as noted above, are suitable for the packaging of meat, they are normally not so suitable for the packaging of fruit and produce, which is easily bruised inside the package by sharp rib contours, and between packages as they are stacked. To meet this particular need, trays of the type disclosed in the Reifers et al. U.S. Pat. No. 3,756,492 have been utilized. These latter produce trays work well and have been successful, but there is still room for improvement.